Recently, interactive projection devices have been developed to allow human users to use a projection surface both for viewing content, such as computer graphics, video, and the like, as well as for inputting information into the system. Meetings and presentations are often carried out using such interactive projection devices. By using a white board as a screen for projection, comments and underline can be directly written down on the white board, and immediately created on the whiteboard so as to organize a discussion.
An interactive projection device typically includes a projector for projecting images on a screen, and a camera for capturing images from the screen. However, because of independent operations of the projector and the camera, position detection errors inevitably occur in respect to changes of the relative position between the projector and the camera, necessitating additional calibration and refocus processes for the camera.
FIGS. 1A-1C are diagrams illustrating position detection errors in a conventional projection device. In FIG. 1A, displacement between a projector 110 and a camera 120 leads to displacement between a projected area ‘AP’ of the projector 110 and a captured area ‘AC’ of the camera 120. Accordingly, an additional calibration is performed on the camera so as to expand the captured area ‘AC’ to cover the projected area ‘AP’, as shown in FIG. 1B. However, once the projector 110 is refocused and the relative position between the projector and the camera changes, displacement between the projected area ‘AP’ and the captured area ‘AC’ will appear again as shown in FIG. 1C, and therefore requires re-calibration and refocus processes for the camera 120.
U.S. Pat. No. 6,979,087 to Honig, et al. titled “Display System with Interpretable Pattern Detection” describes a display system with interpretable pattern detection. However, the display system employs a projector and an image sensor that are separated by different optical axes. As described above, calibration is required to eliminate the displacement between projected and captured images, and the image sensor has to be refocused when the projector is refocused.
In another aspect, China Patent Publication No. 201307347 to Hong-Xian Hao titled “Interactive Computer Projection Teaching Management Device and System” discloses an indicating end to substitute a laser pointer commonly used in conventional projection devices so as to provide advantages of interactive computer teaching. Additionally, U.S. Pat. No. 7,410,260 to Mehrl titled “Use of a CCD Camera in a Projector Platform for Smart Screen Capability and Other Enhancements” discloses an optical projection and capture system and focuses mainly on recognition of an interaction signal. However, these techniques both require an external input device to point to a screen and thus have limited applications.
In another aspect, China Patent No. 1,749,942 to Meng Fanhua, et al. titled “Optical Device for Interactive Projection Display” proposes an optical device for interactive projection display with a beam splitting mirror in the projection optical axis to make the photoelectronic detector and the projection lens of the optical device coaxial. Additionally, U.S. Patent Publication No. 20080051135 to Destain; Patrick R.; et al. titled “Combination Camera/Projector System” discloses a combination camera/projection system including a single polarizing beam splitter (PBS). Additionally, U.S. Pat. No. 6,830,345 to Kamm, et al. titled “Imaging Device” discloses an imaging device including a common polarization selective beam splitter device. However, these techniques may have a low signal to noise (S/N) ratio due to the imperfect splitting performance of the single beam splitting mirror, beam splitter, or beam splitter device.
On the contrary, U.S. patent application Ser. No. 09/365,210 to Brennesholtz entitled “Efficient Two-Panel Projection System employing Complementary Illumination” describes an imaging system having four PBSs. Additionally, U.S. Patent Publication No. 20090079969 to Chou; Sen-Yih; et al. titled “Method and apparatus for scatterfield microscopical measurement” discloses an apparatus for scatterfield microscopical measurement utilizing two PBSs. Additionally, U.S. Patent Publication No. 20090028032 to Toishi; Mitsuru; et al. titled “Hologram Reproducing Apparatus” discloses a hologram reproducing apparatus with four PBSs. However, the above conventional techniques are all applied to different technical fields from that of the subject invention and only incorporated herein for reference.